Rock wool (referred to incorrectly as mineral wool in our earlier British Patent Applications Nos 9600164.9 and 9614048.8) comprises glassy fibres having good thermal insulation properties, which may be in the form of a mat or loose wool or may be compressed to form eg boards and pipe sections. Rock wool is used as a growing medium in the technique of hydroponics, and is used in the construction industry as a thermal and acoustic insulating material, eg under the name Rocksil (Rocksil is a Trade Mark of Owens Corning).
Rock wool is typically produced by smelting minerals containing silica, alumina, magnesium, calcium and iron, which are mixed with coke fuel. The mixture is smelted to a high temperature, about 1500.degree. C., generally in a special furnace known as a cupola. The resulting melt is blown in a fibrous form over rollers. It is a characteristic of the known production process that as much as 30% of all production is sub-standard and is in globular or spherical form, known as shot or overshot, rather than the desired fibrous form. The shot is relatively dense and sandy in consistency, and its particulate nature is such that it cannot be mixed with the cupola input material for reprocessing. This arises because the cupola based process only functions properly when the size of the raw materials is such as to permit the free passage of air and gases through the cupola during the smelting process. As a result, the shot currently constitutes a non-reusable waste material that requires disposal.
At present waste rock wool shot is mainly disposed of by landfill, but in the current climate of rising environmental standards and the imminent increase in the cost of landfill, this approach is becoming less attractive.
It has been proposed to compress the waste material into solid blocks such as briquettes, weighing 125 to 250 grams or more, but the sandy consistency has meant that the resulting briquettes have possessed very poor strength and have tended to crumble without the addition of a binder. Binder materials so far proposed comprise molasses, dextrin and natural latex, which also create further environmental problems and do not contribute thermal stability. Moreover, the cost of these binder materials is not insignificant which would add to the cost of the overall process and would inevitably be reflected in the price of the rock wool.
The present invention is based on use of alternative binder materials that enable, inter alia, an alternative approach to be taken to the treatment and handling of rock wool shot.